Technical Field
Aspects of the example implementations relate to a phantom for radiation oncology used in X-ray radiation therapy, and a phantom control system and control method.
Related Art
In radiation (X-ray) therapy, in which a patient is irradiated with X-rays, the X-rays are first generated by an X-ray generator and are then focused onto an affected area of the patient by a collimator (an apparatus with a focusing function), while being shaped to conform to the shape of the affected area. In this process, it is necessary to correctly irradiate only the abnormal cells (tumor cells, for example), while keeping irradiation of neighboring normal cells to a minimum.
However, the shapes of tumors observed in the human body vary considerably. Also, since the patient subject to X-ray radiation is a living organism, the body moves slightly even when the patient is lying on a couch and at rest. The body motion is caused by motions of the internal organs, for example, by the lungs and the heart, and the body moves four-dimensionally (4D) in various patterns. Here, 4D motion means motion in three-dimensional coordinate space and in time.
For example, in the case of radiation therapy of a lung tumor, the lung tumor moves with the lungs during respiration. To dynamically capture movement of the tumor by 4D-CT (Four-Dimensional Computer Tomography), and to correctly radiate an X-ray beam to the tumor itself, a marker is set close to the tumor. The motion of the marker is captured by the X-ray perspective image, and then an X-ray is radiated.
As already described, it is necessary first to study the 4D motion of a patient, and then to check if the motion is properly tracked and if the X-ray is radiated at the proper point. Since the check is carried out during X-ray radiation, a human being cannot be used as the target.
Accordingly, a phantom that simulates a human being to a greater or lesser degree of accuracy is used. In some case, however, because the phantom does not show any motion, the body motion previously described is not taken into account when estimating the X-ray dosage. In those cases where the phantom does model body motions, the modeling is unidirectional and/or incapable of expressing internal motions.
Also, in previous phantoms, it has been difficult to reproduce electron density (gray scales of CT image) of human body. Accordingly, in a prior inspection of the treatment of the treatment plan using the previous phantoms, reproducibility of absorbed dose at a tumor location is unsatisfactory.